A natural gas hydrate refers to a cage-like crystal matter generated by a natural gas and water at a certain temperature and pressure and can exist in the nature in a variety of ways. Due to the huge reserves and the clean and efficient properties, the natural gas hydrate is considered as a potential alternative energy. If the natural gas hydrate can be effectively, quickly and economically exploited, the increasing energy pressure can be alleviated. Therefore, research on a natural gas hydrate exploitation method is an important issue to be urgently solved in the field of oil and gas engineering.
The existing exploitation methods can be generally divided into three categories: a thermal exploitation method, a chemical agent exploitation method and a pressure reducing exploitation method. The pressure reducing exploitation method is proposed earliest and is considered to be a simple, economical and effective method, which is mainly used for reducing the pressure of a hydrate reservoir to be lower than the balance decomposition pressure of the natural gas hydrate so as to promote the natural gas hydrate to decompose, and the exploitation of a free gas below a hydrate layer is an effective method for reducing the reservoir pressure. However, the pressure reducing method also has the defects of slow hydrate decomposition rate and long exploitation period. Meanwhile, since the natural gas hydrate mainly exists in deepwater seabed sediments, how to reduce the pressure is a difficult problem. A numerical simulation research finds that due to the permeation of seawater on the hydrate reservoir in a pressure reducing process, a huge water yield severely influences the pressure reducing efficiency and the hydrate decomposition rate. At present, the research on the natural gas hydrate exploitation technology is mainly achieved by laboratory simulation, but the existing experiment equipment is relatively simple, a constant volume method is mainly adopted to synthesize and decompose the hydrate, which is hard to truly simulate actual marine geological conditions, in particular, due to the lack of experiment equipment used for simulating a penetration process of seawater and an aquifer on the natural gas hydrate reservoir, an experimental simulation result is not matched with a numerical simulation result and the hydrate exploitation process under actual geological conditions is difficult to truly reflect.